The present invention is directed to a device for drilling an undercut in a borehole in a receiving material, such as concrete, rock, masonry and the like. The device includes a housing arranged to abut against the receiving material. A guide sleeve with an eccentric bore parallel to the axis of the sleeve is located in the housing and an eccentric bushing is supported in the bore so that it can be rotated through an angle of approximately 180.degree.. A drive shaft with a cutter head at one end extends through and is rotatably supported in the eccentric bushing.
Mainly, boreholes with undercuts are formed for receiving correspondingly shaped dowels for anchoring the dowels in a positively locked manner. The formation of a borehole with an undercut is, however, very expensive if known processes and devices are used.
A device for the formation of an undercut borehole is known from EP-A 0 231 720, however, the device is quite cumbersome to handle. In this device, an eccentric bushing is supported eccentrically in the guide sleeve and is turned by a worm drive. A drive shaft with a cutter head at its leading end is supported in the eccentric bushing and is moved into an eccentric position by the turning motion. As a result, the cutter head penetrates into the wall of the borehole. Subsequently, the guide sleeve along with the eccentric bushing and the rotatably supported drive shaft is turned through 360.degree. forming a full circumferentially extending undercut in the wall of the borehole. Next, the eccentric bushing must be returned through 180.degree. so that the cutter head is located in a centered position for removing the device from the borehole.